Molecular Orientation of E7 Liquid Crystal in POLICRYPS Holographic Gratings: A Micro-Raman Spectroscopic Analysis

Abstract

Micro-Raman Spectroscopy was used to determine the orientation of the E7 nematic liquid crystal molecules inside the POLICRYPS (POlymer LIquid CRYstal Polymer Slices) holographic gratings. The POLICRYPS grating was analyzed after defining the Raman features of each single component of the system: i.e the random aligned nematic liquid crystal E7 and Norland Optical Adhesive (NOA-61). Among the Raman bands of the liquid crystal molecules, a specific one was selected, which exhibits strong anisotropy of the Raman tensor. The modulation of its intensity, depending on the sample orientation with respect to the laser polarization, provided the experimental evidence about the orientation of the E7 molecules, which occurred to be perpendicular to the polymeric slices.